Microwave grounded cathode circuit



United States Patent 'MICROWAVE GROUNDED CA THODE CIRCUIT Norman T. Lavoo, Watervliet, .N. Y., and Robert L. Kyhl, Broolrline, Mass., .assignor to General Electric Company, a corporation of New York Application December '28, 1956, Serial No. 631,2:17

Claims. (Cl. :179-171) Our invention relates to improved high frequency electric discharge-device circuits *and more particularly to improved grounded cathode or cathode return circuits.

In oscillator or amplifier circuits employing wire circuits with lumped impedances, both grounded grid (grid return) and grounded cathode .(cathode return) circuits have been used extensively. With the development of the disk seal :type of tube for high frequency applications and particularly the planarelectrode type of disk sea'l tube,

the grid return or grid separation type of circuit found wide acceptance for use in circuits having distributed impedance characteristics. -Further improvements in these tubes, particularly with respect to shorter transit times,

has made it desirable to utilize the cathode return type of circuit which, within certain limitations due to the effect of lead in inductance and transit times, offers substantial superiority over the grid return type of circuit with respect to power gain.

It is accordingly an important object of our invention 'to provide an improved cathode return type of circuit with particular reference to "power gain attainable at m'oderately'high frequencies in circuits of space resonant or distributed characteristic type.

It is another object of our invention-to provide an improved "output coupling for a grounded cathode circuit having an output anode-cathode circuit including 'a shielded parallelpair of conductors.

In accordance with the illustrated embodiment of our invention, a planar electrode type of electric discharge device is connected with a circuit including a grid-cathode circuit and a grid-anode circuit, each of the concentric type and each extending oppositely along the axis of the discharge device. The outer conductor of these concentric circuits is provided, in the region of the discharge device, with an opening through which a pair of parallel conductors extend. These conductors terminate at their inner ends on the inner conductors of the cathode-grid and grid-anode circuits respectively and are, therefore, connected'respectively with'the cathode and anode. These parallel conductors are shielded by a surrounding conductor supported from the outer conductor of the cathodegrid and grid-anode circuits. The parallel conductors are terminated by a short circuiting member which is adjustable in position along these conductors. The output is obtained by two oppositely phased coupling loops extending through opposite sides of the shielding conductor. This arrangement provides coupling to the desired mode; that is, the mode in which the currents in the two parallel conductors are in phase opposition at the points of intersection of the conductors with any transverse plane along the length of the line. Coupling to the second mode existing in the parallel line, namely the mode in which the currents in the two conductors are in phase coincidence, loads the grid-anode or neutralization resonator andirnpairs neutralization.

The novel features which We believe characteristic of our invention are set forth with particularity in the appended claims. Our invention itself, however, will be understood best by reference to the following detailed description taken in connection with the accompanying .drawingin which Fig. 1 is an elevational view in section of .a cathode return circuit embodying our invention;

Fig. 2 is a sectional view taken along the line 22 of Fig. 1 and showing more completely the outputcircuit, and

Figs. 3a and 3b illustrate diagrammatically the H' lines and E lines for the two modes of a parallel transmission line.

Referring now to Fig. .1 of the drawing, we have shown our invention embodied in a high frequency amplifier circuit of the cathode return type. The circuit includes the electrodes of a planar-type electric discharge device, illustrated somewhat schematically and including a planar anode 1, a planar cathode 2 and a planar grid 3 interposed between the anode and cathode. The envelope of the discharge device includes two similar flanged metal cylinders 4 and 5 which are positioned with their respective flanges registering and between which the grid 3 is clamped. The outer-ends of the cylinders .4 and 5 are closed .by annular insulating members 6 and 7 of glass or other suitable insulating material which are bonded to the inner surfaces of cylinders 4 and 5 and the outer surface of cylindrical conductors 8 and 9 and which provide the externally accessible electrical connections for -the anode and cathode, respectively. In the interest of simplifying the drawing, inner conductors 10 and 11 of the grid-anode resonator 12 and cathode-grid resonator 13 have been shown as integral extensions of the anode and cathode lead-in conductors 8 and 9 respectively. It will be readily apperciated that conductors 10 and 11 will usually be separately formed and suitably connected to conductors 8 and 9. It will also be appreciated that a suitable heater element (not shown) is supported adjacent the cathode surface 2 and provided ductors and the walls of recesses 15 and 16 provide the outer conductors of the grid-cathode and grid-anode resonators respectively. As illustrated, the outer conductors are secured to .the opposite faces 17 and 18 of the body 14 by means of insulating washers 21 and 22 respectively, which are secured to the body 14 by means of suitable screws 23. The insulating washers 21 and 22 engage suitable flanges .24 and 25 formed on the inner ends of the conductors 19 and 20 and which are in turn insulated from the body 14 with respect to the direct current voltages by means of insulating spacing washers 26.

The recesses 15 and 16 terminate short of the center of the block 14 to provide a flange 27 which is apertured to receive and support the discharge device with the grid terminal thereof conductively connected with the body .14 and accordingly connected with the conductors 19 and 20 with respect to high frequency currents.

The grid-cathode or input resonator is provided with a suitable input supply circuit illustrated in the drawing as comprising a concentric transmission line including outer conductor 28 and an inner conductor 29 terminatingin a probe 30, capacitively coupling the input line to the grid-cathode resonator.

As illustrated in the drawing, the grid-anode or.neutralizing resonator is provided with a suitable conducting plunger 31 to provide for the tuning of this circuit. The input circuit may likewise be provided with a tuning plunger which has been omitted from the drawing in the interest of simplification.

In accordance with an important aspect of the present invention, the output of the amplifier circuit is derived from a parallel type transmission line anode-cathode circuit, by a circuit coupled to only the plus-minus mode of the parallel transmission line. As shown in the drawing, the anode-cathode circuit is provided by parallel conductors 32 and 33, connected at their inner ends with the anode and cathode conductors 8 and 9, respectively. These conductors extend through a generally elliptical slot 34 provided in the side wall of the conducting body 14. This slot communicates with the exterior of the body through a cylindrical counterbore 35 which provides the inner portion of the shielding conductor of the parallel transmission line. This conductor is extended by means of a conducting cylindrical member 36, terminating at its inner end in a flange 37, secured to the body 14 by means of suitable screws 38. As illustrated in the drawing, the anode-cathode resonator is providedwith an adjustable conducting tuning plunger 39. In order that the parallel conductors 32 and 33 and alsocylinder "36 may operate at different direct current potentials, the plunger 39 does not directly contact conductors 32 and '33.

It is connected to these conductors by means of disks 39a and 39b respectively which are capacitively coupled to plunger 39 through insulating disks 39c. Independently operable shorting conducting plates 40 and 40a contact the parallel conductors 32 and 33, respectively and are supported from the plunger 39 by means of an insulating operating rod 41. These plates are connected together with respect to high frequency currents by insulating disk 40b.

Before considering in detail the manner in which the output is obtained from the anode-cathode line just described, reference may be had to Figs. 3(a) and 3(b) for a better understanding of the modes of operation of a parallel conductor transmission line. As shown in Fig. 3(a), in the plus-plus mode, the currents plane in the two conductors at any transverse are in phase and the H lines extend around the conductors in the same directions. oppositely from the two inner conductors. in Fig. 3(b) for the plus-minus mode, the one to which we wish to couple in order to obtain the maximum power gain with the cathode return circuit without impairing the operation of the grid-anode or neutralization reso-.

nator, the currents in the two conductors at any transverse plane are in phase opposition and the H lines extend in opposite directions around the conductors. The E lines, as shown, extend in the same direction, that is, to the left, as illustrated in Fig. 3(b).

Maximum energy may be supplied to the output circuit by providing an oppositely phased coupling to the parallel conductors. In the modification shown in the drawing, this is accomplished by coupling an output concentric transmission line shown in Fig. 2 at 42 by means of oppositely directed coupling loops 43 and 44 to the field surrounding the parallel anode-cathode conductors 32 and 33, through transmission line branches 43 and 44 of equal electrical length. As will be apparent to those skilled in the art, other arrangements may be made for eflfectively coupling with the plus-minus mode. For example, if in-phase coupling loops are employed, or if probe couplings are used, it is necessary that the half wave length difference which is desired in the coupling 'circuitbe introduced in the form of an additional half wave length of transmission line in one of the arms of In operation the plunger 39 is adjusted to a position spaced approximately one-fourth wave length from the couplings 43 and 44. If the output circuit is coupled to the plus-plus mode, it efiectively loads the grid-anode Also, the E lines are symmetrical and extend As shown or neutralization resonator and impairs its operation with resultant instability of the circuit. By coupling to the plus-minus mode, this difliculty is eliminated and the advantages of the cathode return type of circuit at moderately high operating frequencies are realized in a distributed circuit. 7

While we have described a particular embodiment of our invention, it will be apparent to those skilled in the art that changes and modifications may be made without departing from our invention in its broader aspects and we aim, therefore, in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters of Patent of the United States is:

1. A high frequency system comprising an electric discharge device including cathode, grid and anode terminals supported in'axially spaced and mutually insulated relation in the order named, concentric resonators extending in opposite directions from said device, each of said resonators including a hollow cylindrical outer conductor and an inner conductor, said outer conductor being connected to said grid terminal and said inner conductors being connected with said anode and said cathode respectively, said outer conductor defining an opening through the outer wall of said resonators and a pair of spaced parallel conductors extending through said opening and coupled to the inner conductors of said resonators, a hollow conductor surrounding said parallel conductors and a pair of output circuits coupled to said parallel conductors in oppositely phased relation.

2. A high frequency system comprising an electric discharge device including cathode, grid and anode terminals supported in axially spaced and mutually insulated relation in the order named, concentric resonators extending in opposite directions from said device,'each of said resonators including a hollow cylindrical outer conductor and an inner conductor, said outer conductor being connected to said grid terminal and said inner conductors being connected with said anode and said cathode respectively, said outer conductor defining an opening through the outer wall of said resonators and a pair of spaced parallel conductors extending through said opening and coupled to the inner conductors of said resonators to provide a parallel conductor transmission line, a hollow conductor surrounding said parallel conductors and means coupling an output circuit to said parallel conductors.

3. A high frequency system comprising an electric discharge device including cathode, grid and anode terminals supported in axially spaced and mutually insulated relation in the order named, concentric resonators extending in opposite directions from said device, each of said resonators including a hollow cylindrical outer conductor and an inner conductor, said outer conductor being connected to said grid terminal and said inner conductors being connected with said anode and said cathode respectively, said outer conductor defining an opening through the outer wall of said resonators and a pair of spaced parallel conductors extending through said opening and coupled to the inner conductors of said resonators to provide a parallel conductor transmission line, a hollow conductor surrounding said parallel conductors and output circuit means coupled to said parallel conductors to extract energy from the plus-minus mode of oscillation of said parallel conductors.

4. A resonator structure providing axially aligned hollow cylindrical conductors and a hollow cylindrical conductor extending in a direction perpendicular to said axially aligned conductors, said axially aligned conductors having an opening in the Walls thereof communicating with the interior of said perpendicular conductor, an electric discharge device supported within said aligned conductors in the region of said opening and including externally accessible cathode, grid and anode terminals,

central conductors within said aligned hollow cylindrical 5 conductors connected with said cathode and anode respectively and forming with said aligned conductors a pair of concentric resonators, said grid terminal connecting with said aligned hollow cylindrical conductors with respect to high frequencies, a pair of parallel conductors extending through said opening and coupled to said lastmentioned inner conductors to provide an anode-cathode output circuit surrounded by said perpendicularly extending outer conductor and output circuit means coupled to said parallel conductors in oppositely phased relation.

5. A resonator structure providing axially aligned hollow cylindrical conductors and a hollow cylindrical conductor extending in a direction perpendicular to said axially aligned conductors, said axially aligned conductors having an opening in the walls thereof communicating with the interior of said perpendicular conductor, an electric discharge device supported within said aligned conductors in the region of said opening and including externally accessible cathode, grid and anode terminals, central conductors within said aligned hollow cylindrical conductors connected with said cathode and anode respectively and forming with said aligned conductors a pair of concentric resonators, said grid terminal connecting with said aligned hollow cylindrical conductors with respect to high frequencies, a pair of parallel conductors extending through said opening and coupled to said lastmentioned inner conductors to provide an anode-cathode output circuit surrounded by said perpendicularly extending outer conductor, an output circuit, and means coupling said output circuit to said parallel conductors comprising a pair of concentric lines of equal electrical length and a pair of oppositely directed inductive coupling loops.

References Cited in the file of this patent UNITED STATES PATENTS 2,523,307 Kandoian Sept. 26, 1950 

